Method and apparatus for feeding wood chips into a chip bin

ABSTRACT

The invention concerns a method for feeding chips into a chip bin or corresponding, the chips in said method being forced to move substantially horizontally as a plug filling the cross-section of the transfer space. The chip plug is formed and maintained at a part of the length of the transfer space with chips forced batchwise to the transfer motion.

The present invention concerns a method and a respective feedingapparatus for feeding chips into a chip bin. The object of theimplementation of the method and the construction of the feedingapparatus is to prevent problems discovered with the methods of priorart and the feeding devices implementing the same. These problemsinclude, among others, flow of gases from the bin upstream against thefeeding direction of the chips in cases where the chips are treated inthe bin with steam or process gases for heating the chips. Also dustformation of the chips when filling the bin has caused problems in thedevices of prior art, because the dust also travels upstream against thedirection of flow of the chips.

Problems have occurred when the feeding of the chips to the bin has beenperformed by means of a screw conveyor extending substantially to thefeed opening of the bin. The screw conveyor operates characteristicallyso, that there is a lot of free space on the upper part of the conveyor,through which the gases and dust can be carried upstream against thefeeding direction. The screw conveyor also loosens the conveyed chipswhereby a dense bed is not formed. For avoiding this problem, there hasbeen suggested a stop baffle acting against gravity at the dischargingend of the screw conveyor, meant to be closed after the chip flow stops.A chip feeding apparatus based on the described operation is disclosedi.a. in the U.S. Pat. No. 5,766,418. There have been, however,deficiencies discovered in the operation of the baffle, closing has notbeen reliable and discharging flows have occurred against the feedingdirection in the functional situations. Another possibility of using ascrew conveyor is to throttle the chip flow at the discharging end ofthe screw in order to form a chip plug, but this has been discovered tocause chip damages deteriorating the pulping and defibration to beperformed afterwards.

Attempts to solve the dust and gas problems have also been made by usingcompartment feeders as feeding devices of the chip bins. The problemswith these devices is the wear caused by the chips and foreign agentscoming with the chips, causing leakages, whereby the problems remain thesame.

It has been discovered that the upstream flows against the feedingdirection of the chips can be eliminated by means of a method inaccordance with the present invention and a feeding apparatusimplementing the same. Further, the operation in accordance with theinvention, as well as the implementing apparatus, do not cause problemsfor the chips to be fed.

When implementing the method in accordance with the invention, a plugmoving substantially in the horizontal direction is formed of the chipsto be fed, said plug filling the cross-sectional transfer space,preferably for a remarkable length of the transfer space. The chip plugis formed and maintained by means of chips forced to move batchwise,whereby the forcing period extends over a part of the length of thespace of progress. This operation causes that the plug moves in thefeeding direction only when new chips to be fed come to the pushingdevice to fill up the plug and push it forward for the length of thefilling up in the feeding direction. When the incoming chip flow forsome reason stops, the chip plug is immovable, as the filling up batchesare missing. The chip plug formed in the transfer space, however,preventing the flow of the gases. The feeding situation continues whenthe chip flow returns to the feeding equipment.

The batches forming the chip plug in the transfer space can be formed asone batch having a cross section substantially corresponding to thecross sectional area of the transfer space. Alternatively, the feedbatches can be formed as a plurality of batches distributed over thecross section of the transfer space and being moved to the feedingdirection preferably at least partly nonsimultaneously. The abovementioned substantially horizontal travel of the plug must be in thisconnection interpreted rather freely, chiefly excluding thegravitational travel only. The path of travel can slightly differ fromthe horizontal direction, declining or inclining, taken into account,that there must be caused a certain hindrance to motion for the plug forproviding the required density of the plug. Naturally the length of thetransfer space also has influence on the hindrance to motion exerted tothe plug.

The basic parts of the apparatus are the transfer channel and the inletconnection opening to one end thereof, and the outlet connection at theother end thereof, leading to the chip bin. Between these twoconnections the transfer channel has a certain length, that is at leastin the same range as the diameters of the inlet connection and theoutlet connection. For providing the transfer motion of the chips in thetransfer channel from the inlet connection to the outlet connection,there are transfer elements of chips located in the transfer channel.These transfer elements are according to the characterizing features ofthe invention, pushing means performing reciprocal movement in thedirection of the transfer channel, located onto the opening area of thetransfer channel, having a length of stroke substantially shorter thanthe transfer channel.

With these pushing means the chips falling from the inlet connection tothe transfer channel are pushed forward in the feed direction of thechannel, whereby the chips form a natural chip plug filling thecross-section of the channel and forms an obstacle against the gases anddust coming from the bin against the flowing direction.

The invention is described in more detail in the following, withreference to the enclosed drawing, wherein

FIG. 1 shows a schematic drawing of the feeding apparatus in accordancewith the invention, as a cutaway side view, and

FIG. 2 shows a cutaway perspective view of the apparatus.

The apparatus shown in FIG. 1 comprises a transfer channel 1 havingpreferably a rectangular cross-section and a length bigger than theheight of the cross section. An inlet connection 2 of chips is connectedto said channel, at one end thereof, on the upper side, where the chipsto be fed are brought with conveyors known in the art, and spilled intothe transfer channel. At the opposite end of the transfer channel 1there is a discharge connection 4, through which the chips are spilledor discharged from the transfer channel 1 to be led to the chip bin, notshown in the drawing.

At the first end of the transfer channel, to the area, where the inletconnection 2 opens to the transfer channel 1, there are located chiptransfer elements 3, comprised of a plurality of pushing means 5performing reciprocal movement on the first end of the transfer channel.The a total pushing surface of the pushing means 5 correspondssubstantially to the cross-sectional area of the transfer channel. Thepushing means are preferably acting alternately, whereby at lease one ofthem is moving out of phase with the others, preferably so that at leastone pushing means moves backwards while the others move in the feedingdirection.

The operational motion of the pushing means can be achieved in a simpleand reliable way by means of a crank mechanism 6 operated by a suitabledrive equipment. Also a cylinder-piston mechanism, arranged for eachpushing means separately or shared by a plurality of pushing means isusable as a drive system. The cylinder-piston mechanism can be pneumaticor hydraulic. A hydraulic and a pneumatic drive gives more freedom forarranging the mutual movements of the pushing means, because eachpushing means can be controlled independently from the other pushingmeans. With the drive equipment a stroke length S can be provided forthe pushing means, having a length of a range of about ½ of the transferchannel length L. The stroke length S of the pushing means is of thesame range of the height of the pushing means.

For ensuring the formation of the chip plug in the transfer channel,there can be arranged a stopper 7 delimiting the upper surface of theship flow, said stopper 7 having preferably an adjustable location. Thisstopper can act as a densing means of the chip plug in the transferchannel 1, when the chips are moving under it forced by the pushingmeans 5. The transfer channel can also be formed converging in thefeeding direction by mounting one or some of its walls inclined. Theinclination of the walls can also be adjustable for adapting theoperation of the apparatus for different situations.

The transfer channel can be divided with walls 9 parallel to thedirection of the channel into compartments 8 each of them having theirown pushing means 5. The pushing means 5 has substantially the samewidth and height as the compartment 8. The walls act for their part asguides for the pushing means, but the guiding can also be implementedwith rails mounted on the bottom of the channel and adapted to therespective grooves in the pushing means 5.

The chip feeding apparatus in accordance with the present invention isalso self-adjusting in the operation. In case the chip flow from theinlet connection stops, the pushing means 5 are not able to push newmaterial to the transfer channel 1, but the chip plug made by thepushing means 5 remains in the transfer channel 1 preventing the gasesand dust from coming to the inlet connection 2. Remaining of the chipplug dense in the transfer channel can be assisted with an apparatus,where the pushing means 5 are hydraulic or pneumatic separately used,whereby each pushing means are movable to its most extended position tosupport the chip plug.

At the discharge end of the transfer channel 1 there may be provided agravity-operated hatch system 10, intended for acting as a non-returnvalve in situations, where the chip space coming after the dischargeconnection 4 is clearly pressurized, and the chip feed for some reasonstops from the inlet connection 2.

The density of the chip plug sets substantially to the same in differentloading situations of usage, whether there is more or momentarily lesschip feed. The feeding amount is adjusted by means of the speed controlof the crank mechanism 6 or correspondingly by means of a periodicaloperation of the hydraulic or pneumatic drive.

1. A method for feeding chips into a chip bin or a corresponding vessel,the chips in said method being forced to move substantially horizontallyas a plug along a transfer space, the space having a length and across-section, and an inflow at one end of the length as well as anoutflow at the opposite end of the length, wherein the chip plug isformed and maintained at the inflow by subjecting a reciprocatingpushing action in the transfer direction on the chips, using a strokefor the reciprocating pushing action reaching to a distance in thetransfer direction, which distance is a minor part of the length of thetransfer space.
 2. A feeding apparatus for feeding chips into a chip binor a corresponding vessel, said apparatus comprising an essentiallyhorizontal chip transfer channel having a length, a cross-section, aninflow end and an outflow end, a chip inlet connection opening to thetransfer channel at the inflow end, elements for transferring the chipsin the transfer channel from the inflow end to the outflow end, and adischarge connection leading at the outflow end from the transferchannel to the chip bin or a corresponding vessel, wherein the chiptransfer elements are pushing means located at the inlet connection, thepushing means being equipped to perform a reciprocal movement in thelength direction of the transfer channel, and the length of stroke ofthe pushing means being a minor part of the length of the transferchannel.
 3. A feeding apparatus in accordance with claim 2, wherein thestroke length of the pushing means is ⅕ to ⅓ of the length of thetransfer channel.
 4. A feeding apparatus in accordance with claim 2,whereby the pushing means are arranged to operate substantially to coverthe total cross section of the transfer channel.
 5. A feeding apparatusin accordance with claim 4, wherein each pushing means is arranged tooperate in a separate compartment extending along the length of thetransfer channel and having substantially the width of the pushingmeans.
 6. A feeding apparatus in accordance with claim 3, wherein thepushing means are arranged to operate substantially to cover the totalcross section of the transfer channel (1).
 7. A feeding apparatus inaccordance with claim 2, wherein the pushing means are arranged tooperate out of phase with each other.
 8. A feeding apparatus inaccordance with claim 3, wherein the pushing means are arranged tooperate out of phase with each other.
 9. A feeding apparatus inaccordance with claim 4, wherein the pushing means are arranged tooperate out of phase with each other.
 10. A feeding apparatus inaccordance with claim 5, wherein the pushing means are arranged tooperate out of phase with each other.
 11. A feeding apparatus inaccordance with claim 6, wherein the pushing means are arranged tooperate-out of phase with each other.